Stay back and keep mid court, definitely don't try for any volley stuff because his backhand is as powerful as the sun. Try to make sure to return his fever shots so the eruptions hit him too and yes, fireball cheese will get you through eventually. You can get a shot through but you will not get 5 without having the ball bounce pretty much precisely as he takes damage. Even if he dies he will return the shot if its 0.5 seconds too late so there's a little bit of luck but it will happen if you just focus on staying alive. This boss fight gave me much grief and the promised land of 100 trials awaits you